This invention relates to a keeper lock for a zipper-type slide fastener. More particularly, the invention relates to a single key-operated keeper lock having a cylinder lock mechanism which constitutes the primary locking structure, and also having a locking bar which cooperates with the cylinder lock mechanism to perform an auxiliary locking function.
U.S. Pat. No. 3,070,986 describes a keeper lock of the type with which the present invention is concerned. The keeper lock, having a cylinder lock mechanism, is designed for use in securing slide fasteners on bags or other containers or enclosures, as noted in the patent, and, with certain modifications, the lock continues in use. One modification, of interest in connection with the present invention, involves the provision at the base of the lock cylinder of a pair of axially outwardly projecting flanges defining a recess between them, which recess serves to receive a flat spring pinned to the barrel in which the cylinder is received. A stem on the spring extends into the keyway of the cylinder. Insertion of a key into the cylinder both adjusts the tumblers and engages the stem to remove the spring from the recess, thereby enabling the lock cylinder to be rotated and the lock to be opened. The structure serves, inter alia, to increase the pick-resistance of the lock, inasmuch as it is necessary to perform a function of the key additional to the conventional tumbler adjustment function, in order to open the lock without the key.
The modified patent structure has the disadvantage in providing pick-resistance that the flat spring may be bent out of shape by a tool inserted through the lock, so that only the tumblers perform a locking function. Moreover, when the spring is moved out of the recess, it and the stem projecting into the lock cylinder therefrom are moved in a curved path, so that the stem may catch on other structure and hold the spring out of the recess, where it will not perform a locking function.
Another single key-operated lock having a cylinder lock mechanism and also employing a locking bar to perform an auxiliary locking function is disclosed in Chicago Lock Co. Catalog 176, copyright 1976, on page 26 thereof, wherein the structure is referred to as "Chicago Double Bitted Special Coincidental Locking Feature." In this structure, the locking bar is carried by the lock cylinder, and the locking bar must engage the surrounding barrel in the tumbler grooves. Both the lock cylinder and the surrounding barrel are specially constructed for cooperation with the locking bar.
A keeper lock basically constructed as disclosed in the above-identified patent is a desirable lock, inasmuch as it functions well in its intended applications, and it has a simple and economical structure, in general commensurate with the security required and the cost acceptable in its applications. Nevertheless, it would be advantageous to increase the security of the lock at a relatively low increase in the cost of manufacture.